package com.xizi.秋招笔试;

import java.util.Scanner;

/**
 * @author xizizzz
 * @description: TODO
 * @date 2021-8-11下午 04:12
 */
public class F {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int x = scanner.nextInt();
        int y = scanner.nextInt();
        int m = scanner.nextInt();
        if (x >= m || y >= m) {
            System.out.println("0");
        }
        if (x <= 0 && y <= 0) {
            System.out.println("-1");
        }
        int min = Math.min(x, y);
        int max = Math.max(x, y);
        int res = 0;
        while (max < m) {
            min += max;
            min = Math.min(min, max);
            max = Math.max(min, max);
            res++;
        }
        System.out.println(res);

    }
}
